Ryzen 7 1700 memory speed question

Hi there. A few days ago I rebuilt my computer after the previous motherboard and / or CPU failed. I'd got both second hand for £60 over three years ago, so it did OK I guess. Anyway, I've gone for a Ryzen 7 1700 on a Gigabyte B450 Aorus Pro motherboard, with 16 GB Corsair DDR4 RAM rated at 2666 MHz. The machine is running fine so far with no stability problems at stock settings, but I've found the BIOS and Windows report the RAM is clocked at 2133 MHz. Does anyone know if this is because the CPU has a fixed core clock to memory clock ratio it will run at, meaning I would need to over clock the CPU to get the RAM up to its stock speed? Thanks for any advice.